(a) Field of the Invention
The present invention relates to a level shifter.
(b) Description of the Related Art
An electrical device such as a display device includes a level shifter for changing a level of an input voltage to a level required for driving the display. Particularly, in the case of a polycrystalline thin film transistor (“TFT”) flat panel display, in which driving units for generating electric signals to be applied to pixels are integrated on a substrate, a threshold voltage of the TFTs which form the driving units is high and electric field effect mobility is low, therefore a voltage which is higher than an input voltage should be applied to stably drive the driving units at a high speed.
Flat panel displays may come in several different varieties including liquid crystal displays (“LCDs”), field emission displays (“FEDs”), organic light emitting diode (“OLED”) displays, plasma display panels (“PDPs”), and various other display types. In general, in an active flat panel display, a plurality of pixels are arranged in a matrix form, and an image is displayed by controlling luminance of each pixel according to applied image information.
A driving unit of the flat panel display receives a control signal and a source voltage from a signal controller and generates a scan signal and a data signal to be applied to pixels, and each level of the control signal and the source voltage are obtained by variably converting a level of the input voltage by using a level shifter.
However, conventionally the level shifter performs only a single operation for increasing or decreasing the input voltage, so in order to shift the input voltage in both directions, a complementary level shifter circuit is additionally required.